Soil compaction device having a light detector

ABSTRACT

The invention relates to an operating device which is provided for operating an appliance and which comprises a hand-actuated operating part on which at least one light detector is provided in the gripping area of the hand. The light detector and an evaluating circuit make it possible to detect when a hand is approaching the guide handle or when the hand is gripping the same. The evaluating circuit accordingly activates a control device which optionally places the appliance in operation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to a soil compaction device.

2. Description of the Related Art

To control or steer work equipment, all types of guide handles, controllevers, safety handles, switches, pushbuttons and the like are used.What is common to most of these control elements is that the operatorinitiates the desired action through the introduction of force to acontrol system using his hand. If necessary, other safety elements areprovided that the operator must activate, such as pressure handles orthe like, so as to guarantee that the operator is holding the workequipment securely, thus preventing danger caused by the work equipmentwhen it malfunctions or fails to operate. Moreover, there are alsotactile, capacitive, ultrasound and infrared sensors that determine theexistence or proximity of the hand to the operating element.

The various control devices of this type have different disadvantages:in the case of safety handles, switches or pushbuttons, a movingactuator has to be held by hand, which leads to a tiring of the handover time. Furthermore, a solid hand grip, which is usually required,can lead to the transmission of vibrations to the hand and arm of theoperator. The sensors are partially sensitive to noise or cannot be usedwhen using gloves.

In FR-A-2 674 077, for example, an optical switch control device isdescribed that can adjust to changing surrounding light conditions.

In U.S. Pat. No. 6,319,250, an equipment guide handle is disclosed thatis steered by placing both hands of the operator on the handle in orderto guarantee that the hands are located on the handle.

OBJECTS AND SUMMARY OF THE INVENTION

The objective of this invention is to provide a soil compaction devicethat can reliably determine that a hand is located at a control element,in particular a guide handle, even with heavy shaking without having toapply any force by hand.

This objective is met according to the invention by a soil compactiondevice with the features of patent claim 1. Further advantageousdevelopments of the invention can be found in the dependent claims.

According to the invention, a soil compaction device has a guide handleprovided with at least one light detector in the area gripped by thehand, said light detector emitting a signal corresponding to thebrightness (brightness signal), wherein the light detector is coupled toan evaluation circuit that can evaluate the brightness signal in such away that when a prescribed brightness threshold is exceeded or is notmet, a control signal is sent to a control unit of the device. Also, thebrightness threshold can be variably adjusted by the evaluation circuitaccording to the surrounding conditions, with a surrounding lightdetector that is coupled to the evaluation circuit being providedoutside the grip area of the hand to determine the surroundingconditions.

This type of soil compaction device makes it possible, by merely movingthe operator's hand to the vicinity of the control element (guidehandle), to change the amount of light incident on the light detector,which then detects the change and reports it to the evaluation circuit.If the operator grips the control element with his hand, the lightdetector is blacked-out and for the most part separated from the outsidebrightness given off by the sun or by an artificial light source. Byblacking out the light detector, thus changing the brightness signal, itcan be reliably determined that a hand has approached the controlelement.

It is preferred that the light detector operate according tophotoelectrical or photo-resistive principles, so that the brightnesssignal changes in strength when light hits it.

In the process, the light detector contains no light-emitting element,i.e. no additional light source, at the control element, whichconsiderably increases its sensitivity to noise.

As already mentioned, the brightness threshold is variably adjustable bythe evaluation circuit depending on the surrounding conditions. For thispurpose, the evaluation circuit can be coupled to an additionalsurrounding light detector that detects the absolute surroundingbrightness. When the brightness determined by the light detector at thecontrol element falls below a brightness threshold determined accordingto the absolute brightness, this can be interpreted by the evaluationcircuit as the approach of a hand to the control element. This preventsinfluences caused by the surrounding brightness since it can varygreatly (twilight, direct sunlight).

In an especially advantageous embodiment of the invention, a number oflight detectors are provided at the control element at a minimum of twopoints in the grip area for both hands. In this way, the evaluationcircuit coupled with the light detectors is able to determine that bothhands are on the control element, which is prescribed for certain workequipment for safety reasons.

The soil compaction device is, for example, a tamper, a vibration plateor a vibration roller. Soil compaction devices are subject to severeloads during rough construction site use, resulting in the rapid failureof numerous known control devices, or resulting in the need forconsiderable design effort. However, the light detectors proposedaccording to the invention can be well protected from the environmentand protected against contamination or destruction by integrating theminto the control element.

BRIEF DESCRIPTION OF THE DRAWING

This and other advantages of the present invention are explained in moredetail below with the help of an example illustrated in the drawings inwhich:

FIG. 1 schematically shows a schematic plan view of soil compactiondevice guided by a guide handle on which a control element constructedin accordance with the present invention is attached: and

FIG. 2 schematically shows a plan view of the guide handle of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 shows a schematic plan view of a guide handle 1, which is thecontrol element attached at a point not shown to a soil compactiondevice 10 (FIG. 1) to be operated.

There are a number of light detectors 2 attached to the guide handle 1at points where the operator commonly holds the guide handle 1 with bothhands. Suitable as light detectors 2 are light-sensitive elements suchas photo diodes, photo transistors, light-sensitive resistors (LDR,light-dependent-resistor) and similar systems that change electricallydue to optical excitation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The light detectors 2 are powered by an evaluation circuit 3, which alsoevaluates the brightness signals given off by the light detectors 2. Inthe evaluation circuit 3, the brightness signals are compared to abrightness threshold. Depending on the results of the comparison, i.e.if the prescribed brightness threshold is not met or is exceeded, acorresponding control signal is sent to a control unit 4 of the soilcompaction device. This control signal can, for example, correspond tothe signal that is produced when securely holding a conventional safetyhandle.

What is claimed is:
 1. A soil compaction device comprising: a guidehandle provided with at least one light detector in an area gripped by ahand, said light detector emitting a signal corresponding to abrightness, wherein the light detector is coupled to an evaluationcircuit that can evaluate the brightness signal in such a way that whena prescribed brightness threshold is either exceeded or is not met, acontrol signal is sent to a control unit of the soil compaction device,and wherein the brightness threshold can be variably adjusted by theevaluation circuit according to surrounding conditions via a surroundinglight detector that is coupled to the evaluation circuit and is providedoutside the grip area of the hand to determine the surroundingconditions.
 2. A soil compaction device according to claim 1, whereinthe light detector at the guide handle does not contain a light-emittingelement.
 3. A soil compaction device according to claim 1, wherein thelight detector at the guide handle is a photodiode, a phototransistor ora light-sensitive resistor.
 4. A soil compaction device according toclaim 1, wherein a number of light detectors are provided at the guidehandle at a minimum of two places in grip areas of both hands.
 5. A soilcompaction device comprising: a guide handle; at least one lightdetector located on said guide handle in an area configured to begripped by a hand of an operator, said light detector emitting a signalcorresponding to a brightness; a control unit; and an evaluation circuitthat is coupled to said light detector, wherein said evaluation circuitis configured to evaluate the brightness signal in such a way that whenthe brightness signal either exceeds or falls below a prescribedbrightness threshold, a control signal is sent to the control unit ofthe soil compaction device; and a surrounding light detector that iscoupled to the evaluation circuit, that is provided outside the griparea of the handle, i.e., and that is configured to determinesurrounding conditions, wherein the evaluation circuit can variablyadjust the brightness threshold according to the surrounding conditionsdetected by the surrounding light detector.
 6. A soil compaction deviceaccording to claim 5, wherein the light detector at the guide handledoes not contain a light-emitting element.
 7. A soil compaction deviceaccording to claim 5, wherein the light detector is selected from thegroup consisting of a photodiode, a phototransistor and alight-sensitive resistor.
 8. A soil compaction device according to claim5, wherein a plurality of light detectors are provided at a minimum oftwo places on the guide handle that are configured to be in areasgripped by both hands of an operator.